This invention relates to devices for connecting together frame bars of the kind having cross-sectionally T-shaped grooves on side surfaces.
Elongated construction materials (herein referred to as frame bars) having cross-sectionally T-shaped longitudinal grooves on side surfaces are known, as sold, for example, by NIC Autotec, Inc. of Toyama, Japan. According to a conventional method of connecting a plurality of such frame bars parallel to and next to one another, the head of a bolt and a nut are inserted into the T-shaped grooves of two frame bars placed adjacent to each other so as not to fall off through the openings of the grooves as they are engaged together. In the case of very long frame bars, holes will have to be drilled additionally in the middle, and a bolt and a nut are similarly used to fasten the middle sections of the frame bars, too. This connecting method is inconvenient because the bolt or the nut must be rotated inside a groove and they must be placed near the end surfaces of the frame bars. In other words, the bolts and nuts cannot always be placed at optimum positions from the point of view of the structural strength. Moreover, a connection by a bolt and a nut is known to be weak against shearing force in a direction of the joined surfaces.